正则替换图片路径

 string yourhtml = @"<img alt= ""test"" alt=network-adaptors.jpg src= ""/IT/cr/2007/0704/3441139462.jpg "" style= ""border:0px solid #000; "" _extended= ""true "">  
<img alt= ""test"" alt=network-adaptors.jpg src= ""/IT/cr/2008/34/3656462.jpg "" style= ""border:0px solid #000; "" _extended= ""true "">  ";
            string str = "http://www.baidu.com/";
           
            yourhtml = Regex.Replace(yourhtml, @"(?i)(?<=<img\b[^>]*?src=\s*(['""]))(.*/)+(?=[^'""/]+\1)", "http://www.baidu.com/$2", RegexOptions.IgnoreCase);